The field of the invention is systems and methods for magnetic resonance imaging (“MRI”). More particularly, the invention relates to systems and methods for magnetic resonance spectroscopy and spectroscopic imaging.
Although two-dimensional or even higher dimensional nuclear magnetic resonance (“NMR”) spectroscopy includes a wide range of well-established methods in chemistry and structural biology, through which a wealth of structural information can be obtained, the development of in vivo multi-dimensional MR spectroscopy (“MRS”) lags behind. Here multi-dimensional spectroscopy refers to multiple spectral dimensions as opposed to multiple spatial dimensions. For in vitro applications, especially in the case of crowded biomolecular systems such as proteins or brain biopsies, multi-dimensional MRS methods are crucial for disentangling overlapped signals and obtaining unambiguous assignments and structural constraints. A similar situation exists in vivo, with many metabolites overlapping in a reduced chemical shift range. Although there are considerably less visible in vivo metabolites than there are amino acids in a protein, the overlapping may be as severe in vivo because of reduced chemical shift dispersion and lower spectral resolution. Hence, complex fitting routines have been developed to extract the metabolic information from one dimensional in vivo spectra.
Two dimensional in vivo MR spectroscopy could help in reliable assignment, quantification, and perhaps, identification of new metabolites. To date, despite early interest, the number of two-dimensional NMR experiments adapted for in vivo MRS has been limited. This is largely due to the challenges of in vivo MRS, such as restrictions on lower radio frequency (“RF”) power deposition and specific absorption rate (“SAR”), reduced signal-to-noise ratio (“SNR”) from the adapted methods, shorter acquisition times, and the hardware of the clinical scanners.
It would therefore be desirable to provide a method for performing two-dimensional MRS that can provide clinically relevant spectral information about a subject with adequately high levels of SNR while maintaining low levels SAR and RF power deposition.